In recent years, the use of compact circuitry has made possible the downsizing of electronic hardware and its subsequent proliferation into a great number of new locations and uses. However, both the downsizing of hardware and its proliferation into many new locations has exacerbated the already existing problem of static electromagnetic radiation or noise emission. Noise emission by circuits within an item of hardware can interfere with other electronic devices within the same item of hardware or can interfere with electronic devices within other proximate items of hardware. The smaller the item of hardware, the more severe the problem with internal interference and the more difficult it is to solve such internal interference by conventional techniques. Similarly, where an item of hardware is used in a great number of differing locations, the chances that it will interfere with or conversely be interfered with by a second item of hardware are greatly increased.
Methods of shielding circuitry from interference and preventing noise emission are well known. Most such methods require that a conductive shield encase the circuitry which is to be protected or which is the source of noise. These conductive shields may be made from metal or from a conductive plastic such as a conductive fiber filled plastic. Shielding by these methods, however, will prevent maximum equipment downsizing due to the bulk of the shielding material, or will prevent internal shielding because only a single shielding layer is placed about the entire item of hardware.
Therefore, it is an object of the present invention to produce multi-layer circuit boards which emit reduced levels of noise and which are less susceptible to interference from other noise sources.
It is another object of the present invention to produce multi-layer circuit boards which are self-shielding.
It is yet another object of the present invention to produce a board where adjacent conductor runs of a conductive patter do not couple.